The invention relates generally to a UV sensitive composition, and dosimeters for measuring UV radiation, and more particularly to dosimeters that are adapted to measure UV-C radiation.
It is generally known that reducing the exposure to oxygen of oxygen sensitive articles maintains and enhances the quality and shelf life of the article. For instance, reducing the oxygen exposure of oxygen sensitive food products in a packaging system maintains the quality of the food product and avoids food spoilage. Reduced oxygen exposure keeps the product in inventory longer, thereby reducing costs incurred from waste and having to restock.
One method of reducing oxygen exposure is to incorporate an oxygen scavenging composition into the packaging structure, such as in a film or tray. Oxygen scavenging compositions are compositions that consume, deplete, or reduce the amount of oxygen in a given environment. There are a wide variety of different compositions that can be used in oxygen scavenging applications. Exemplary compositions are described in U.S. Pat. Nos. 5,211,875; 5,350,622; 5,399,289; and 5,811,027 to Speer et al. and WO 99/48963 to Cai et al. The oxygen scavenging compositions can be “triggered” by exposing the composition to a radiation source, such as actinic radiation, having sufficient power for a sufficient amount of time to initiate oxygen scavenging.
Methods of triggering oxygen scavenging compositions typically use low-pressure mercury germicidal lamps that have an intensity output from about 5 to 10 mW/cm2. These lamps are commonly referred to as germicidal since the principal emission is at 254 nm. A dosage of UV-C light of about 100 to 1600 mJ/cm2 is typically needed to trigger oxygen scavenging. For details on preferred methods for activating such oxygen scavenging compositions at point of use, see Speer et al., U.S. Pat. No. 5,211,875, Becraft et al., U.S. Pat. Nos. 5,911,910, and 5,904,960, and co-pending applications U.S. Ser. No. 09/230,594 filed Aug. 1, 1997, and Ser. No. 09/230,776 filed Jul. 29, 1997, and U.S. Pat. No. 6,233,907 (Cook et al.), all of which are incorporated herein by reference in their entirety.
Unfortunately, oxygen scavengers do not always activate on command. This may result from a number of factors, including defective scavenger compositions, inadequate triggering conditions, operator error, or a combination of these or other factors. In many instances, it may not be readily apparent whether the oxygen scavenging composition is defective or whether the failure originated in the triggering equipment. Typically, conventional oxygen scavengers do not themselves visually indicate whether or not they are active. In response to this uncertainty, operators of packaging assembly plants prefer to verify scavenger activity as soon as possible after triggering. The longer a failed triggering attempt remains undiscovered, the more waste and expense is incurred, especially where packaging equipment operates at high speeds.
There are several methods for verifying oxygen scavenger activity. Typically, oxygen concentrations are measured in the package after it has been assembled. This can typically be accomplished by using a probe that measures the oxygen concentration in the package, or with an oxygen indicator that is disposed in the interior of the package, or in the packaging material itself. U.S. Pat. No. 6,689,438 to Kennedy et al. describes a luminescent compound that can be incorporated into a film or article. The luminescent compound is adapted to detect and measure oxygen concentration levels in the packaging.
If the oxygen scavenging activity is too low it will be necessary to determine whether the problem is associated with the compound or the triggering equipment. Typically, this requires the operator to stop production and review the current status and operation of the triggering equipment. In many cases, an operator may waste time in verifying that the triggering unit is functioning when the problem is with the compound itself. To quickly eliminate the triggering equipment as a source of the problem, it has been proposed to incorporate fiber optic monitors into the trigger equipment. The fiber optic monitors would measure the output of the lamps. The monitors could then be checked to verify that the triggering equipment is working properly. Unfortunately, fiber optic monitors are typically cost prohibitive and may require retrofitting the existing UV triggering equipment. In some instances, it may not be feasible to use the fiber optic monitors with the existing equipment.
Thus, there remains a need in the art for a significantly faster method and article for verifying that oxygen scavenging compositions have been exposed to a sufficient dosage of UV-C radiation.